1. Field of the Invention
The present invention relates to a probe for electrical impedance measurement and more particularly to a surgical needle construction for providing electrical impedance measurements to confirm or monitor the location of the needle tip within a patient""s body.
2. Description of the Related Art
Surgical needles, such as trocar needles, are known and used during surgical procedures to access target body tissue or a target body cavity for observation, treatment, biopsy, and the like. Typically, trocar needles comprise an outer cannula and an inner stylet. The stylet typically has a sharp, pointed tip for skin and tissue penetration and the outer cannula defining a channel to provide subsequent access for endoscopic examination, biopsy, or the like. Sometimes the cannula has a sharp distal edge, in which case the stylet may be a blunt obturator and/or inner cannula.
The insertion of conventional trocar needles can be problematic. Indeed, the surgeon must estimate the location of the trocar needle tip during insertion. This may result in the undesirable accidental puncture of anatomical structures as the needle is being inserted and the surgeon may have difficulty in confirming arrival at a desired anatomical target.
Because conventional trocar insertion methods are imprecise and may be risky, it is an object of this invention to provide a surgical needle, such as a trocar needle, that allows the surgeon to monitor the path of needle insertion, to confirm needle insertion into a desired anatomical target, and/or to identify the nature of cells surrounding the tip of the trocar needle.
The foregoing object is realized by providing a two-part trocar needle designed to acquire impedance measurements at its tip. Such impedance measurements characterize the biological substance at the needle tip. Thus, the impedance measurements provided by the trocar needle of the invention may be used to confirm needle insertion into a desired anatomical target and/or to identify the nature of the biological material surrounding the tip of the needle, to monitor the path of the needle, or for diagnostic purposes. In urology, an impedance sensor provided in accordance with the invention may be used to confirm needle insertion into the urinary tract and for localizing, e.g., renal cell carcinoma.
Thus, the foregoing and other objects are realized in accordance with the present invention by providing a surgical probe for obtaining impedance measurements, comprising a hollow trocar sleeve having an electrically conductive portion defining a first electrode adjacent its distal end, and means, e.g., the wall of the trocar sleeve or a portion thereof, or a lead therein, for electrically connecting the electrically conductive portion to a proximal end portion of the sleeve; a stylet having an electrically conductive portion defining a second electrode adjacent its distal end, and means for electrically connecting the electrically conductive portion to a proximal end portion of the stylet; an electrical insulator disposed between the trocar sleeve and the stylet; and an impedance meter electrically coupled to the electrodes, for indicating the impedance of a biological substance contacting the electrodes. It should be recalled, that as noted above, a trocar needle assembly that has two (or more) parts may have a sharp pointed stylet and/or an outer cannula terminating in a sharp edge. Where the outer cannula is adapted to piercing the material through which the trocar is inserted, the inner stylet can be but is not necessarily pointed; it may be a blunt obturator and/or inner cannula. Therefore, references to stylet herein are intended to refer to the structure disposed within the outer cannula, but are not to be limited to a sharp, pointed component unless so specified.
Also and alternatively, the objects of the invention may be realized by providing a diagnostic impedance measuring system comprising: an elongate tissue-penetrating needle, a first portion of the distal end of said tissue penetrating needle being electrically conductive; at least one electrode structure disposed adjacent the distal end of the needle and axially spaced from the first portion thereof, the first portion and the at least one electrode being electrically connected to an impedance measuring device for measuring an electrical impedance of a biological substance contacting said first portion and said electrode.
The objects of the invention are also realized by inserting an impedance probe of the type described above into a patient""s body, measuring the impedance between the electrodes, and confirming the location of the distal tip (within a region of interest and/or the identity of the biological substance at the tip of the probe from the measured impedance.